Conventionally, an exhaust pipe structure for an internal combustion engine has been known in which an exhaust purifying catalyst device is arranged in the vicinity of the internal combustion engine within an engine room. With this exhaust pipe structure, due to restrictions in layout, a cylindrical exhaust purifying catalyst device is arranged in a state orienting the center axis line thereof in a substantially vertical direction. For this reason, the exhaust pipe extending from the internal combustion engine side greatly bends downwards after extending in a substantially horizontal direction, and is connected to a upper end of the exhaust purifying catalyst device.
However, with the above-mentioned such exhaust pipe structure, the flow of exhaust gas is concentrated on the outer side of the curved part of the exhaust pipe, and the exhaust gas of concentrated flow flows into the exhaust purifying catalyst device. For this reason, since the exhaust gas is not flowing uniformly into the exhaust purifying catalyst device, a rapid temperature rise of the exhaust purifying catalyst has been difficult, and it has not been possible to sufficiently exhibit the purifying performance of the exhaust purifying catalyst device. Depending on the case, the exhaust purifying catalyst has deteriorated due to the uneven flow of exhaust gas. Therefore, an exhaust pipe structure has been proposed that provides, to the inner wall of an exterior portion of the above-mentioned curved part, a gas rectifying part for causing the flow of exhaust gas to approach the inner side (for example, refer to Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-17018